With the continuing shrink of silicon device sizes, the processing speed of digital signal processors and micro controllers keeps on growing. However the current consumption is rising too. In many electronic systems high processing speed is only needed during short periods of operation. The rest of the time such systems are in a sleep mode or standby mode at a very low activity level. However the systems cannot be fully shut off as they must be able to resume full operation in a very short period of time. In particular as a result of high leakage currents typical for silicon devices there is still significant supply current being drawn by the systems in sleep mode or standby mode. It will be appreciated that this is not desired from the point of view of energy conservation. Moreover, due to this inefficient use of available energy, many of these type of applications must be powered by mains voltage or a by a durable, large capacity power source that enables operation over a sufficiently long period of time. Battery operation is often not possible, or results in the application being large and bulky, and as therefore difficult to handle or install.